ON POISONS. 29 



movements, and the tendency to convulsive muscular action. It is not, in 

 truth, novel to refer these symptoms to the accumulation of carbon in the 

 system ; but, close as the similarity in many respects undoubtedly is in these 

 instances, the disorder in which we have the nearest resemblance, and which 

 seems as if it were its true prototype, is still the Opprobrium Medicorum. 

 We have in the symptoms produced by carbonic acid, the counterpart of those 

 exhibited in epilepsy ; no less instantaneous is the attack of this appalling 

 malady, than are the effects of the sudden closure of the glottis by the irri- 

 tation of the choke damp, or other exposure to fixed air, by persons descend- 

 ing into vats, or breathing the gas given off by fermentation. Plunge an 

 animal into it, or inject it into the veins, and we can at will produce epilepsy 

 with all its terrific features and depressing consequences. 



The curious coincidence of the diminished secretion of this acid from the 

 lungs, towards evening, when the natural tendency to sleep comes on ; the 

 increase in its quantity at day-break, when epileptic seizures are most likely 

 to occur ; the hurried and spasmodic respiration, when it is present in excess, 

 are valid arguments for the belief that it may be an active agent in exciting 

 both healthy and disordered functions. 



Carbonic acid acts upon the medulla oblongata, for it annihilates volition and 

 consciousness, which have their seat in this portion of the nervous centres. 

 The medulla oblongata also, be it observed, is the source of the respiratory 

 movements *. How these are called into action we are yet in doubt ; that 

 they may be excited primarily and throughout life by the stimulus of car- 

 bonic acid, is advanced as a conjecture, which derives abundant support from 

 the analogy of other excretions. 



Minute details would here be out of place, or the quantity of this gas, 

 capable of producing injurious consequences, and the peculiarities of indivi- 

 duals rendering them especially liable to its influence, might be entered into. 

 Suffice it, that extremely minute portions of gaseous bodies, as shown in the 

 instance of the odour of musk, or the fragrance of flowers, is enough to pro- 

 duce the most decided effects. 



It were tedious to enter into collateral inquiry, or to combat objections 

 which may be advanced against the ideas thus submitted to the Association. 

 It is doubtless extraordinary that an acid should be formed in the blood, and 

 given off, instead of combining withthe alkali of the serum. The insensibi- 

 lity of animals confined in nitrogen or hydrogen gases, in which the quantity 

 of carbonic acid nearly equals that by natural respiration, may be otherwise 

 explained ; new combinations may form ; carburetted hydrogen, for instance, 

 may be generated, which would itself poison the animal ; and we should not 

 forget the fact, that the insensibility, occasioned under the circumstances 

 alluded to, is found to be much more easily dissipated than that which arises 

 from the prevention of the escape of carbonic acid from the body. 



From this we might pass on to various spasmodic disorders, but it were 

 perhaps premature to say anything further on this head ; only one more point 

 shall be noticed in connection with this subject, and that is the resemblance 

 in the effects of narcotic poisons to those arising from carbonic acid. Reflec- 

 tions upon these facts have led me to think that tliis gas may play an essential 

 part in the phenomena exhibited by narcotics, a class of substances, the 

 operation of which is so little understood, but the action of which is ob- 

 viously upon the functions of the system, rather than upon the vascularity of 

 its organs. It has long been laid down as a rule, that opium is not to be ex- 

 hibited when the blood is not i^roperly aerated or decarbonised. 



Many experiments have been made by me to ascertain whether any difference 

 * MiUler, pp. 348, 351, 827, 918. 



